This invention concerns apparatuses and a method for xe2x80x9cextractionxe2x80x9d of biomass. This is the extraction of flavours, fragrances or pharmaceutically active ingredients from materials of natural origin (these materials being referred to as xe2x80x9cbiomassxe2x80x9d herein).
Examples of biomass materials include but are not limited to flavoursome or aromatic substances such as coriander, cloves, star anise, coffee, orange juice, fennel seeds, cumin, ginger and other kinds of bark, leaves, flowers, fruit, roots, rhizomes and seeds. Biomass may also be extracted in the form of biologically active substances such as pesticides and pharmaceutically active substances or precursors thereto, obtainable e.g. from plant material, a cell culture or a fermentation broth.
There is growing technical and commercial interest in using near-critical solvents in such extraction processes. Examples of such solvents include liquefied carbon dioxide or, of particular interest, a family of chlorine-free solvents based on organic hydrofluorocarbon (xe2x80x9cHFCxe2x80x9d) species.
By the term xe2x80x9chydrofluorocarbonxe2x80x9d we are referring to materials which contain carbon, hydrogen and fluorine atoms only and which are thus chlorine-free.
Preferred hydrofluorocarbons are the hydrofluoroalkanes and particularly the C1-4 hydrofluoroalkanes. Suitable examples of C1-4 hydrofluoroalkanes which may be used as solvents include, inter alia, trifluoromethane (R-23), fluoromethane (R-41), difluoromethane (R-32), pentafluoroethane (R-125), 1,1,1-trifluoroethane (R-143a), 1,1,2,2-tetrafluoroethane (R-134), 1,1,1,2-tetrafluoroethane (R-134a), 1,1-difluoroethane (R-152a), 1,1,1,2,3,3-hexafluoropropane (R-236ca), 1,1,1,2,2,3-hexafluoropropane (R-236cb), 1,1,1,3,3,3-hexafluoropropane (R-236fa), 1,1,1,3,3-pentafluoropropane (R-245fa), 1,1,2,2,3-pentafluoropropane (R-245ca), 1,1,1,2,3-pentafluoropropane (R-245cb), 1,1,2,3,3-pentafluoropropane (R-245ea) and 1,1,1,3,3-pentafluorobutane (R-365mfc). Mixtures of two or more hydrofluorocarbons may be used if desired.
An especially preferred hydrofluorocarbon for use in the present invention is 1,1,1,2-tetrafluoroethane (R-134a).
It is possible to carry out biomass extraction using other solvents, such as chlorofluorocarbon (xe2x80x9cCFC""sxe2x80x9d) or hydrochlorofluorocarbons (xe2x80x9cHCFC""sxe2x80x9d) and/or mixtures of solvents.
Known extraction processes using these solvents are normally carried out in closed-loop extraction equipment. A typical example 10 of such a system is shown schematically in FIG. 1.
In this typical system, liquefied solvent is allowed to percolate by gravity in downflow through a bed of biomass held in vessel 11. Thence it flows to evaporator 12 where the volatile solvent vapour is vaporised by heat exchange with a hot fluid. The vapour from evaporator 12 is then compressed by compressor 13: the compressed vapour is next fed to a condenser 14 where it is liquefied by heat exchange with a cold fluid. The liquefied solvent is then optionally collected in intermediate storage vessel (receiver) 15 or returned directly to the extraction vessel 1 to complete the circuit.
There are particular problems when the biomass is a liquid (typically aqueous) form. Examples of liquid biomasses include, but are not limited to, coffee and orange juice. Liquids containing solid biomass particles present similar difficulties. We refer to such biomasses herein as xe2x80x9cliquid entrainedxe2x80x9d biomasses.
Hydrofluorocarbon (HFC) solvents have been found to be effective in extracting such biomasses. An example of a suitable HFC solvent is 1,1,1,2-tetrafluoroethane, sold as xe2x80x9cR-134axe2x80x9d by the KLEA division of Imperial Chemical Industries plc. It would be desirable to provide an apparatus and method capable of continuous extraction of liquid or liquid entrained biomass using e.g. 1,1,1,2-tetrafluoroethane in liquid form.
According to a first aspect of the invention there is provided apparatus for extracting biomass from a liquid biomass supply. The apparatus comprises a hollow vessel containing a liquid, liquid or liquid-entrained biomass being supplied at or near a first side of the vessel and a liquid solvent being supplied at or near a second, opposite side of the vessel such that a stream of solvent passes in one direction through the vessel and a stream of biomass passes as a countercurrent through the vessel, so that biomass extract becomes entrained with the solvent. An outlet for biomass is at or near the second side of the vessel, and an outlet for solvent/extract mixture is at or near the first side of the vessel. A separator is connected to the solvent/extract outlet for separating solvent and extract from one another.
This apparatus advantageously allows intimate mingling of the biomass and the solvent so that the solvent efficiently strips the desirable components from the biomass and entrains them to a further location for separation of the solvent and biomass from one another.
The use of countercurrent flows makes the apparatus suitable for the continuous processing of liquid or liquid-entrained biomass. Conveniently in the apparatus the separator includes a rectifier for rectifying the solvent and separating therefrom the extract, a compressor, and a condenser connected in series, whereby the separator generates substantially uncontaminated solvent in liquid form. These features advantageously separate the desired biomass extract from the solvent whereby the extract is available for further use.
In the apparatus the separator includes a rectifier for rectifying the solvent and separating therefrom the extract, a compressor, and a condenser connected in series, whereby the separator generates substantially uncontaminated solvent in liquid form. The apparatus also includes pipework for supplying at least some of the substantially uncontaminated solvent from the condenser to the hollow vessel in a substantially closed loop circuit that includes the said vessel. This advantageously allows recycling of recovered solvent for contact with further biomass.
In preferred embodiments the separator includes a rectifier for rectifying the solvent and separating therefrom the extract, a compressor, and a condenser connected in series, whereby the separator generates substantially uncontaminated solvent in liquid and wherein the condenser includes first and second condenser ages connected in series, the second condenser stage operating at a lower temperature than the first stage and both condenser stages supplying substantially uncontaminated solvent to the hollow vessel. This is because there are sometimes residual inerts (air, carbon, dioxide, etc) in the aqueous feed stream of biomass. The solvent entrains some of these inert compounds to the condenser. Condensation in the presence of inerts is sometimes difficult. The second condenser stage advantageously separates inerts from the solvent.
The second condenser stage preferably operates at a lower temperature than the first stage. This removes heat from the solvent/inert compound mixture.
Even using a two-stage condenser, some uncondensed vapours may remain. Therefore the second condenser stage advantageously includes a vent for venting uncondensed vapours therefrom.
Preferably the vent is connected to an adsorbent filter that adsorbs solvent in the vented vapour. This advantageously recovers yet more of the solvent.
An example of a suitable adsorbent filter is a bed of activated carbon.
The separator as earlier defined may advantageously have a rectifier (still) for rectifying the solvent and separating therefrom the extract, a compressor, and a condenser connected in series. The separator generates substantially uncontaminated solvent in liquid form and the rectifier includes a still connected to the solvent/extract outlet of the hollow vessel. This still includes a heater for heating any solvent/extract mixture therein to a higher temperature than the solvent dewpoint. An outlet for solvent in vapour form is connected to supply such solvent to the suction side of the compressor, and a drain is provided for extract in liquid form.
Conveniently the still includes a vent and a reflux condenser forming part of the vapour path to the vent. In a preferred embodiment the reflux condenser operates at a higher temperature the solvent dewpoint and at a lower temperature than the mass extract dewpoint. Consequently the ref lux condenser recondenses any biomass fragrance compounds which undesirably distil from the still as a result of the heating mentioned in the last paragraph.
The countercurrent flow established in the hollow vessel entrains some solvent with the liquid biomass. Consequently the hollow vessel includes a biomass outlet which is connected in series to a heatable check tank, and thence to a further condenser for condensing solvent vaporised on heating of the tank. The further condenser includes an outlet for condensed solvent, the outlet being connected to supply solvent condensed in the further condenser to the hollow vessel. These advantageously permit recovery of solvent from the depleted biomass.
The solvent recovered from the depleted biomass may be recycled into the main solvent closed loop for further contact with biomass.
The check tank includes an outlet for liquid biomass residue. The biomass residue may, if necessary, undergo further solvent contamination. It may then be suitable for example animal feeds and landfill operations.
In particularly preferred embodiments the hollow vessel is an upright, elongate vessel through which a biomass stream rises and a solvent stream descends.
An alternative arrangement is one in which the hollow vessel is or includes a mixer-settler unit in which solvent and biomass streams flow in countercurrent.
In practice, there may be a series of mixer-settler units connected in series to define a multi-stage hollow vessel or a plurality of vessels.
Another arrangement is one in which a high intensity mixing device, e.g. a static mixer or inline jet spray mixer, is used to effect the contact and promote mass transfer. Typically such an arrangement could use a gravity setting tank, advantageously however an enhanced separation technology could be used. Examples of high intensity separation technologies include hydrocyclones or centrifugal separators, through which the working liquid, having acquired kinetic energy, may be passed. Various devices such as pumps may be used to impart kinetic energy to the working liquid.
The advantages of using e.g. an inline static mixer coupled with a hydrocyclone (or set of hydrocyclones arranged as desired) are that the inventory of solvent in the system can be reduced, and that the size of the extraction plant can be reduced to a bubble column and gravity settler. In addition the use of high intensity mixers reduces the potential for bypassing/short circuit flow of one of the phases, which could occur in a bubble type contactor.
According to a second aspect of the invention there is provided a method of extracting biomass wherein the biomass is in liquid or liquid-entrained form. The method comprises in a hollow vessel containing liquid, establishing countercurrent flows of liquid solvent and the biomass so that the solvent strips extract from the biomass, and passing the liquid solvent containing extracted biomass to a separating vessel. The solvent is biomass extract is drained from the separating vessel. The solvent evaporated from the extract in the separating vessel, and the is passed in vapour form to means for condensing the solvent, to a heatable check tank, and thence to a further condenser for condensing solvent vaporised on heating of the tank. The further condenser includes an outlet for condensed solvent, the outlet being connected to supply solvent condensed in the further condenser to the hollow vessel, and the check tank includes an outlet for liquid biomass.
This method is advantageously effective in extracting biomass in liquid (typically aqueous) form.
It is particularly preferable that the described method be carried out in a closed loop circuit. This permits efficient recovery of solvent, whose disposal would otherwise present problems.
A further, advantageous feature of the method that permits efficient recovery of solvent following practising of the method, is that the step of condensing the solvent includes the sub-steps of compressing the solvent in vapour form and condensing the solvent.
A still further advantageous feature of the method that permits efficient recovery of solvent following practising the method, is that the step of condensing the solvent includes the sub-steps of compressing the solvent in vapour form and condensing the solvent, and wherein the step of condensing the solvent includes two stages of condensation.
The method also advantageously includes the steps of passing depleted biomass to a further separator and separating further solvent from the biomass in a further separator. This permits recovery of solvent from the depleted biomass.
In particular when practising the method using the apparatus as defined herein, it is advantageous that one of the countercurrent flows occurs under gravity. This reduces the energy consumption of the apparatus.
Alternatively when practising the method using high intensity mixing and separation technologies, gravity may be used at the designer""s choice, however the technology need not rely on use of gravity to separate the liquid. In this case (where gravity is not used to drive flow) the energy consumption may be higher (because of the pumping work used) but as the equipment will in general be much smaller there will normally stilt be all economic benefit.